1. Field of the Invention
The present invention relates to a high density semiconductor device having a semiconductor chip mounted thereon. The present invention also relates to a COB (Chip On Board) substrate, a TAB (Tape Automated Bonding) substrate and a lead frame.
2. Description of the Related Art
FIG. 7 is a plan view of a conventional COB substrate. A die pad 1 for mounting a semiconductor chip is formed on a substrate body 5 of a substantially rectangular shape. A plurality of inner leads 2 are disposed around the die pad 1. Further, a plurality of outer leads 4 corresponding to the inner leads 2 are disposed on the edges of a pair of longer sides 5a and 5b of the substrate body 5. The corresponding inner leads 2 and the outer leads 4 are connected to one another by wiring patterns 3 formed of a conductive material, such as copper. The die pad 1 is generally a rectangular shape, the die pad 1 having the sides that are parallel to the sides of the substrate body 5.
The semiconductor chip (omitted from illustration) having a plurality of electrode pads is mounted on the die pad 1 of the foregoing COB substrate, the electrode pads and the inner leads 2 being electrically connected to one another by wires (omitted from illustration). Then, the semiconductor chip, the die pad 1, the inner leads 2 and the wires are sealed with resin or the like as a packaged semiconductor device.
In a case where the plurality of the outer leads 4 are, in an unbalanced manner, disposed along the longer sides 5a and 5b of the substrate body 5 as shown in FIG. 7, portions A and B, in which the wiring patterns 3 for connecting the inner leads 2 and the outer leads 4 to one another undesirably disposed densely. If the interval between the adjacent wiring patterns 3 is shorter than a predetermined value, short circuiting or cross talk reduces reliability. Therefore, the substrate body 5 must have a large width in order to make the intervals between the wiring patterns in the dense portions A and B longer than a predetermined value. As a result, there arises a problem in the foregoing case that the size of the semiconductor device cannot be reduced. In particular, in a case of a microcomputer, for example, where a semiconductor chip of a type having a multiplicity of electrode pads is mounted, the substrate body 5 must have a sufficiently large size.
It might be considered feasible to employ a substrate with a multiplicity of layers connected to one another by through holes in order to prevent the enlargement of the substrate body 5. However, other problems arise in that the thickness of the substrate cannot be reduced and that the structure becomes too complicated.